1. Technical Field
The present invention, involving Group-III nitride crystal manufacturing methods, relates to epitaxial III-nitride crystal in composites in which the epitaxial crystal has a major surface of plane orientation other than {0001}, designated by choice, and other special properties.
2. Description of the Related Art
Group-III nitride crystals, which are employed advantageously in semiconductor electronic devices including light-emitting devices and semiconductor sensors, are ordinarily manufactured by growing crystal onto the major surface of a sapphire substrate having a (0001) plane major surface, or onto a GaAs substrate having a (111) A-plane major surface, by means of a vapor-phase technique such as hydride vapor-phase epitaxy (HVPE) or metalorganic chemical vapor deposition (MOCVD), or by flux growth or other liquid-phase technique. Consequently, ordinarily obtained III-nitride crystals have a major surface whose plane orientation is {0001}.
With light-emitting devices on substrates that are III-nitride crystal having a major surface whose plane orientation is {0001}, and in which a multiquantum-well (MQW) structure as a light-emitting layer has been deposited on the major surface, the light-emission efficiency is decreased by spontaneous polarization that occurs within the light-emitting layer owing to the III-nitride crystal's <0001> oriented polarity. Consequently, the manufacture of III-nitride crystal having a major surface whose plane orientation is other than {0001} is being sought.
Reference is made, for example, to Japanese Unexamined Pat. App. Pub. No. 2005-162526: The following method has been proposed as way of preparing gallium-nitride crystal having a surface plane orientation of choice, without influencing the plane orientation of the major surface of the substrate. Namely, according to the method disclosed in Pat. App. Pub. No. 2005-162526, a number of rectangular crystal masses are diced from GaN crystal grown by vapor deposition. Meanwhile, a silicon oxide film is coated onto the surface of a separately readied sapphire substrate, and subsequently a number of recesses reaching to the substrate are formed in the film. Next, the numerous crystal masses are embedded into the recesses in a manner such that their top surfaces will have the same plane orientation. Then, by vapor deposition with the crystal masses as seeds, gallium nitride crystal having a surface plane orientation of choice is grown.
With the method in Pat. App. Pub. No. 2005-162526, however, inasmuch as growth of the GaN crystal is carried out with, as seeds, the masses of crystal GaN that have been embedded into the sapphire substrate, due to the disparity in thermal expansion coefficient between sapphire and GaN, fractures and strains appear in the GaN crystal when the crystal is cooled following the growth process, such that GaN crystal of superior crystallinity has not been obtainable.
Furthermore, if III-nitride crystal containing Al—for example, AlxGayIn1-x-yN (x>0, y≧0, x+y≧1)—is grown by the method in Pat. App. Pub. No. 2005-162526, because the Al precursor is not selective with respect to the silicon oxide film, the AlxGayIn1-x-yN grows onto the silicon oxide film as well, and consequently AlxGayIn1-x-yN crystal of superior crystallinity has not been obtainable.